Understanding Linear Dimensions
L + W + H.
What are linear dimensions?
Linear dimensions are the sum of your bag’s Length, Width, and Height. Instead of three separate maximums, the airline publishes one number that your total must not exceed.
Formula: Linear = L + W + H
How to measure correctly
- Measure external size (include wheels and handles).
- Record each side to the widest/thickest point.
- Add the three numbers. If your total is less than or equal to the airline’s limit, you’re within policy.
Typical reference limits
| Bag type | Common linear max (U.S.) | Common linear max (International) |
|---|---|---|
| Carry‑on | ≈ 45 in | ≈ 115 cm |
| Checked (for context) | ≈ 62 in | ≈ 158 cm |
Worked examples
- Example A (inches): Bag is 21 × 14 × 9 in → Linear =
21 + 14 + 9 = 44 in→ typically within a 45‑inch carry‑on limit. - Example B (centimeters): Bag is 55 × 36 × 23 cm → Linear =
55 + 36 + 23 = 114 cm→ typically within a 115‑cm limit.
How this relates to the checker
When an airline posts a linear maximum instead of three separate dimensions, the checker compares your sum against that limit. You’ll see a likely OK when your total is ≤ the limit and a may not fit warning when it exceeds it.
Check your bag Open the Carry‑On Checker
FAQs
Do wheels and handles count? Yes—use external dimensions unless your airline explicitly says otherwise.
Can a bag pass linear limits but fail individual side limits? Yes. Some airlines use either method; always compare against the rule your airline actually publishes.
Why airlines use linear dimensions
Using a single linear measurement simplifies policies and makes baggage sizing easier for both airlines and passengers. It accounts for irregularly shaped bags that might otherwise pass separate length, width and height limits but still protrude in overhead bins. Linear dimensions also align with how baggage is loaded into cargo holds—conveyors and containers have doorways and slots with fixed perimeters.
Airlines that fly mixed fleets with various aircraft types benefit from linear limits: a 45‑inch total may fit a regional jet’s bins and a wide‑body’s overhead compartments alike. For travellers, linear limits provide flexibility. You might have a slightly taller bag that’s narrower than average; as long as the total stays within the limit, you’re compliant.
Linear vs. separate dimension rules
- Separate dimensions: You must meet three individual maximums (e.g., 22 × 14 × 9 in). Exceeding any single measurement means your bag doesn’t comply.
- Linear dimensions: You add up L + W + H and compare to a single figure (e.g., 45 in). You can trade length for width or height as long as the total stays below the limit.
- Hybrid: Some airlines publish both a linear limit and separate maximums. In that case, comply with whichever is stricter.
Packing strategies for linear rules
- Optimize shape: Use bags that are evenly proportioned; a very long and thin bag may waste linear inches that could be used for height or width.
- Compress protrusions: Remove or tuck in straps and handles to reduce total circumference.
- Use soft‑sided luggage: Flexible sides allow you to shave off a few centimeters, especially when not fully packed.
Exceptions & gotchas
- Wheels and handles: Always count them. Airlines rarely exclude them from the measurement.
- Curved bags: Some duffels may fit sizers even if the linear sum slightly exceeds limits because they compress easily—but there’s no guarantee.
- Weight still applies: A bag within linear dimensions can still be denied if it exceeds weight limits on carriers outside the U.S.
More examples
- Example C (inches): Bag is 20 × 13 × 10 in → Linear =
20 + 13 + 10 = 43 in→ well within a 45‑inch limit. - Example D (centimeters): Bag is 60 × 25 × 30 cm → Linear =
60 + 25 + 30 = 115 cm→ exactly at many international limits. Be cautious about bulging pockets. - Example E (hybrid rule): Airline says 45 linear inches and no side over 22 in. Bag is 24 × 10 × 9 in → Linear = 43 in (within limit) but the 24‑in length exceeds the side limit, so it’s noncompliant.
FAQs
Can I rely solely on linear dimensions? Only if your airline uses a linear policy. Some publish both or only separate measurements. Always check your specific flight’s rules.
What if my bag is soft? Soft bags may compress enough to meet linear limits, but there’s no guarantee a gate agent will allow an obviously oversized bag. When in doubt, choose a bag clearly within published limits.
Do checked bags use linear dimensions? Yes—checked luggage almost always has a linear maximum (often 62 inches or 158 cm). Fees apply if you exceed it.